Method of preparing pitch for carbon fiber

ABSTRACT

Disclosed herein is a method of preparing an isotropic pitch for carbon fiber having a high softening point, and more particularly, a method of preparing an isotropic pitch for carbon fiber by mixing petroleum residues with C9 fraction to form a mixture and then heating the mixture to perform heat polymerization. With the method of preparing an isotropic pitch according to the present invention, a separate catalyst is not required, and the isotropic pitch for carbon fiber having a low softening point may be prepared with a high yield even at a relatively low temperature.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method of preparing an isotropicpitch for carbon fiber having a high softening point, and moreparticularly, to a method of preparing an isotropic pitch for carbonfiber by mixing petroleum residues with C9 fraction to form a mixtureand then heating the mixture to perform heat polymerization. With themethod of preparing a pitch according to the present invention, aseparate catalyst is not required, and the isotropic pitch for carbonfiber having a low softening point may be prepared with a high yieldeven at a relatively low temperature.

2. Description of the Related Art

A carbon material has a carbon content of about 95% or more, and carbonmaterials applying various properties of carbon have been developed forvarious uses. As a raw material of the carbon material, all of thecarbon compounds may be used in principle, but an appropriate rawmaterial may be generally selected according to the desired physicalproperties of a final product and manufacturing cost.

Among them, as a petroleum based target raw material, fluidizedcatalytic cracker (FCC), decant oil (DO), pyrolyzed fuel oil (PFO) havebeen spotlighted as a raw material appropriate for high value carbonmaterials such as high strength carbon fibers or needle coke due totheir high aromaticity and low contents of sulfur and insolublecomponents.

According to the related art, a method of preparing an isotropic pitchfrom heavy oil samples such as the PFO has been mainly divided into amethod of heat-treating a precursor pitch from which light oilcomponents are removed at about 400° C. for a long time of about 14hours or more and a method of fractioning the heavy oil samples in anappropriate range using a solvent such as benzene or toluene and thenheat-treating the fractured material.

In this regard, as the carbon materials for various uses has beendeveloped, various methods such as a method of using a catalyticcarbonization reaction, a method of using a vacuum heat treatmentprocess, and the like, have been attempted.

A carbonization process of reforming the heavy oil components such asthe PFO to form a pitch means a series of processes of pyrolyzing oilcomponents, discharging gas and light oil components to the outside ofthe system, and simultaneously cyclizing, aromatizing, andpolycondensing molecules activated by formation of radicals.

Here, while a polycondensation reaction occurs, planar molecules of acondensed polycyclic aromatic group are laminated in parallel with eachother to form a liquid crystal referred to as a mesophase and havingintermediate properties between a solid and a liquid. In this case, thelaminated molecules are optically divided into an isotropic pitch and ananisotropic pitch according to the degree at which the molecules arelaminated or the orientation when the molecules are arranged.

Generally, a pitch based carbon fiber is mainly divided into a liquidcrystal pitch based carbon fiber and an isotropic pitch based carbonfiber according to the kind of pitch, which is a precursor. The liquidcrystal pitch based carbon fiber is prepared using a liquid crystalpitch as the precursor, which is optically anisotropic, and theisotropic pitch based carbon fiber is prepared using the isotropic pitchas the precursor, which is optically isotropic. Describing mechanicalproperties of the prepared carbon fiber, the liquid crystal pitch basedcarbon fiber has high strength and high elasticity, but the isotropicpitch based carbon fiber has general mechanical properties such as lowstrength and low elasticity.

The pitch based carbon fiber is generally prepared by melt-spinning thepitch, which is the precursor, using a spinning machine to fiberize thepitch, oxidation-stabilizing the fiberized pitch at about 150° C. toabout 350° C. under oxidation atmosphere for a predetermined time, andtreating the oxidation stabilized pitch at about 700° C. to about 3000°C. under inert atmosphere for a predetermined time according to the use.

It is known that at the time of preparing the carbon fiber, a preparingcost of the fiber is affected by a cost of the precursor pitch, aspinning property of the precursor pitch, a rate of the oxidationstabilization, a carbonization yield after carbonization, and the like,and in view of a time required for each of the processes, an oxidationstabilization process in which a long reaction time is essentialrequires the longest time. Therefore, it is important to develop aprecursor pitch having excellent oxidation stabilization performance.

As described above, the pitch precursor for the pitch based carbon fiberis mainly divided into the liquid crystal pitch and the isotropic pitch.As a method of preparing an isotropic pitch used as a raw material ofthe isotropic pitch based carbon fiber and having a softening point ofabout 200° C. or more, there are a method of removing low molecularweight components from a coal tar pitch by vacuum distillation andsolvent extraction, a method of condensing low molecular weightcomponents of the raw material by simple heat condensation to convertthe components into high molecular weight components, and a method ofpreparing the isotropic pitch using the two methods described above.However, the isotropic pitch having relatively narrow molecular weightdistribution may be prepared from a raw material having wide molecularweight distribution by these methods, but there are disadvantages inview of homogeneity of the prepared pitch and the spinning propertythereof. For example, the yield may be low and components that may beeasily liquid-crystallized at the time of heating may remain.

A method of preparing a high softening point isotropic pitch, aprecursor of isotropic carbon fiber, by removing quinoline-insolublesfrom a coal tar pitch, which is a raw material, hydrogenating thequinoline-insolubles removed coal tar pitch, and then separatingoxidizing gas has been disclosed in Japanese Patent Laid-OpenPublication No. 1994-256767.

In addition, a method of adding dinitronaphthalene, or the like, at thetime of heat treatment for preparing a pitch in order to increase asoftening point of an isotropic pitch precursor has been disclosed inJapanese Patent Laid-Open Publication Nos. 1993-132767 and 1993-132675.

However, as described above, hydrogenation of the pitch is performed bycarrying out the reaction at a high temperature using an expensivehydrogenation catalyst and then removing the hydrogenation catalyst,which increases the preparing cost of the precursor pitch. Further,nitrogen oxides added in order to increase the softening point isexpensive, and the actual reaction is not homogeneously carried out,such that a melt-spinning property of the prepared pitch precursor maybe deteriorated.

In addition, a method of preparing a high softening point pitch fromnaphtha cracking residues using a complex of BF₃-ether as apolymerization catalyst has been disclosed. However, in this case, sinceBF₃-ether used as the catalyst is significantly expensive, this methodmay not be appropriate for a large scale preparing process.

Recently, a method of preparing an isotropic pitch using a coal tarpitch and petroleum based vacuum residues as raw materials and usinghalogen and a halogen compound as polymerization additives has beendisclosed in Korean Patent Application Nos. 1997-0036064 and1997-0036065.

However, there is a limitation in preparing the isotropic pitchprecursor for carbon fiber having excellent melt-spinning property andoxidation stability and a high carbonization yield under relatively mildconditions with a high yield by the above-mentioned method according tothe related art using the naphtha cracking residues as the raw material.

Particularly, it may be impossible to prepare the high softening pointisotropic pitch precursor for isotropic carbon fiber having excellentproperties as the precursor pitch with a high yield of about 35 weight %or more by using the naphtha cracking residues, particularly, thepyrolyzed fuel oil (PFO) as the raw material and adding halogen and thehalogen compound thereto, followed by simple polymerization and removalof low molecular weight materials.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a method ofpreparing an isotropic pitch for carbon fiber having a high softeningpoint, and more particularly, a method of preparing an isotropic pitchfor carbon fiber by mixing petroleum residues with C9 fraction to form amixture and then heating the mixture to perform heat polymerization.With the method of preparing an isotropic pitch according to the presentinvention, a separate catalyst is not required, and the isotropic pitchfor carbon fiber having a low softening point may be prepared with ahigh yield even at a relatively low temperature.

According to an exemplary embodiment of the present invention, there isprovided a method of preparing a pitch for carbon fiber including: amixing step of mixing petroleum residues with C9 fraction to form amixture; a primary heating step of primarily heating the mixture toinduce a chain extension reaction; a secondary heating step of raising atemperature after the primary heating to remove low boiling pointmaterials; and a tertiary heating step of raising a temperature afterthe secondary heating to induce a condensation reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are scanning electronic microscope (SEM) photographsof carbon fiber prepared using a pitch prepared according to a firstexemplary embodiment of the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Details of embodiments will be described below with reference to theaccompanying drawings.

Various advantages and features of the present invention and methodsaccomplishing thereof will become apparent from the followingdescription of embodiments with reference to the accompanying drawings.However, the present invention is not limited to the exemplaryembodiment disclosed herein but will be implemented in various forms.The exemplary embodiments make disclosure of the present inventionthorough and are provided so that those skilled in the art cancompletely understand the scope of the present invention. Therefore, thepresent invention will be defined by the scope of the appended claims.

Hereinafter, a method of preparing a pitch for carbon fiber according toan exemplary embodiment of the present invention will be described indetail.

The method of preparing a pitch for carbon fiber according to theexemplary embodiment of the present invention may include: 1) a mixingstep of mixing petroleum residues with C9 fraction to form a mixture;and 2) a heating step of heating the mixture. First, 1) the mixing stepof mixing the petroleum residues with the C9 fraction to form themixture will be described.

The petroleum residues and the C9 fraction are put into a reactor andmixed with each other at room temperature.

Here, the petroleum residues are a carbon source of the pitch for carbonfiber, and in the present invention, it is preferable that the petroleumresidues include particularly pyrolyzed fuel oil (PFO) as naphthacracking residues. The PFO, which is generated at a bottom of a naphthacracking center (NCC), has high aromaticity and resin content, such thatthe PFO is appropriate for the method of preparing a pitch according tothe present invention.

The PFO includes various aromatic hydrocarbons, and naphthalene andmethylnaphthalene derivatives account for about about 25-35% thereof.Specific examples of the naphthalene and methylnaphthalene derivativesmay include ethylbenzene, 1-ethenyl-3-methyl benzene, indene,1-ethyl-3-methyl benzene, 1-methylethylbenzene, 2-ethyl-1,3-dimethylbenzene, propylbenzene, 1-methyl-4-(2-propenyl) benzene,1,1a,6,6a-tetrahydro-cycloprop[a]indene, 2-ethyl-1H-indene,1-methyl-1H-indene, 4,7-dimethyl-1H-indene, 1-methyl-9H-fluorene,1,7-dimethyl naphthalene, 2-methylindene, 4,4′-dimethyl biphenyl,naphthalene, 4-methyl-1,1′-biphenyl, anthracene, 2-methylnaphthalene,1-methylnaphthalene, and the like.

In the present invention, the petroleum residues, that is, the carbonsource may be a carbon source from which low boiling point materials areremoved. Since the low boiling point materials are mostly volatilized tothereby not participate in a reaction, a yield as a pitch issignificantly low, and hydrocarbons in the C3 to C8 range belongthereto. In the case of using the carbon source from which the lowboiling point materials are removed, the high softening point pitch maybe prepared with a higher yield.

Meanwhile, the C9 fraction mixed with the petroleum residues so as toreact with the petroleum residues according to the present invention hasmainly 9 carbon atoms, and a specific example thereof may includestyrene, vinyltoluene, indene, a-methylstyrene, orbenzene/toluene/xylene (BTX).

Aromaticity fa of the C9 fraction according to the exemplary embodimentof the present invention may be preferably about 40 to 60%. In the casein which the aromaticity is less than about 40%, raw materials capableof participating in a polymerization reaction are insufficient, suchthat products may be paraffinized, and the yield may be low, and in thecase in which the aromaticity is more than about 60%, there may be aproblem such as rapid coking at the time of heat polymerization.

In the mixture of petroleum residues and the C9 fraction, C9 fractionmay be mixed at a content of about 10 parts to about 50 parts by weight,based on 100 parts by weight of the petroleum residues. In the case inwhich the content of the C9 fraction is less than about 10 parts byweight, based on 100 parts by weight of the petroleum residue, an amountof C9 fraction participating in the reaction is small, such that it maybe difficult to prepare the desired pitch, and in the case in which thecontent is more than about 50 parts by weight, undesired products may beproduced due to a polymerization reaction of an excess C9 fractionitself.

Hereinafter, 2) the heating step of heating the mixture will bedescribed.

The heating step may be performed by multi-step heating in two steps ormore.

More specifically, the heating step may include a primary heating stepof primarily heating the mixture; a secondary heating step of raising atemperature after primary heating; and a tertiary heating of raising atemperature after secondary heating.

In the primary heating step, the mixture of the petroleum residues andthe C9 fraction are primarily heated to induce a chain extensionreaction.

In the primary heating step, double bond chains of the C9 fraction arereleased to form free radicals, such that the chain extension reactionthat the petroleum residues and the chain are extended occurs. Compoundshaving an aromatic structure form bonds via the radicals and have a formin which a plurality of aromatic structures are included in a longchain.

Here, a heating temperature may be preferably about 80° C. to about 100°C. In the case in which the heating temperature is lower than about 80°C., formation of the radical from the C9 fraction may be impossible, andin the case in which the heating temperature is higher than about 100°C., there may be a problem in termination of the chain extensionreaction.

In addition, a heating time may be preferably about 1 hour to about 2hours. In the case in which the heating time is shorter than about 1hour, a sufficient reaction may be impossible, and in the case in whichthe heating time is longer than about 2 hours, the mixture may besolidified during the reaction due to cross-linking of the chainstructure after the reaction is terminated.

In the secondary heating step, after the primary heating is completed,the temperature is raised to remove the low boiling point materials.

Since the coking slowly occurs at a final target temperature of the heatpolymerization (about 360° C.), the coking is decreased and the lowboiling point materials are removed by having an intermediatetemperature section in the secondary heating step.

Here, a secondary heating temperature obtained by raising thetemperature after primary heating may be preferably about 250° C. toabout 300° C. In the case in which the heating temperature is lower thanabout 250° C., it may be difficult to remove the low boiling pointmaterial, and in the case in which the heating temperature is higherthan about 300° C., a coking reaction may occur in addition to removingthe low boiling point materials.

In addition, the heating time may be preferably about ½ hour to about 2hours. In the case in which the heating time is shorter than about ½hour, sufficient removal of the low boiling point materials may beimpossible, and in the case in which the heating time is longer thanabout 2 hours, the coking may occur.

In the tertiary heating step, after the secondary heating is completed,the temperature is raised to induce the condensation reaction.

In the tertiary heating step, the temperature may arrive at a targettemperature of the heat polymerization, and the condensation reaction ofthe petroleum residues and the C9 fraction may occur, such that a pitchhaving a high softening point of about 240° C. or more, preferably about240° C. to about 300° C. may be finally synthesized.

Here, a tertiary heating temperature obtained by raising the temperatureafter secondary heating may be preferably 320 to about 360° C. In thecase in which the heating temperature is lower than about 320° C., thecondensation reaction and removal of the residual low boiling pointmaterial may be impossible, and in the case in which the heatingtemperature is higher than about 360° C., the reactant may be lost dueto a cracking reaction and a rapid coking reaction, and a coking problemmay be generated.

In addition, a heating time may be preferably about 3 hours to about 8hours, but more preferably about 3 hours to about 4 hours. In the casein which the heating time is shorter than about 3 hours, thecondensation reaction and removal of the residual low boiling pointmaterial may be impossible, and in the case in which the heating time islonger than about 8 hours, coking and cracking problems may begenerated.

Hereinafter, preferable Examples of the present invention will bedescribed. The following Examples are provided in order to describe thepresent invention in detail, and the scope of the present invention isnot limited thereto.

EXAMPLE

(1) Preparation of High Softening Point Pitch

After pyrolyzed fuel oil (PFO) as a carbon source and C9 fraction wereput into a reactor and mixed with each other, the mixture was subjectedto primary, secondary, and tertiary heating processes, such that a heatpolymerization reaction was carried out.

After the heat polymerization reaction was terminated, un-reacted orpoorly reacted molecules were removed by passing nitrogen gas at a fluxof 1 L/min for 2 hours, thereby obtaining the desired high softeningpoint optically isotropic pitch.

Reaction conditions of each of the Examples were shown in the followingTable 1.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Mixing ratio 1:0.25 1:0.25 1:0.25 1:0.4 1:0.25 1:0.25 1:1(petroleum residues:C9 fraction) Aromaticity 52 52 44 52 52 81 52 (%) ofC9 fraction Low boiling Removed Not Removed Removed Removed Removed Notpoint removed removed materials in petroleum residue Primary 2 2 1 2 2 20.5 heating time (h) Primary 100 100 100 90 100 100 70 heatingtemperature (° C.) Secondary 1 1 2 1 1 1 1 heating time (h) Secondary260 240 260 260 260 290 260 heating temperature (° C.) Tertiary 4 4 4 35 4 8 heating time (h) Tertiary 360 360 330 360 360 400 360 heatingtemperature (° C.)

2) Softening Point and Yield of the Obtained Pitch

The softening point and yield of the pitch prepared in the Examples weremeasured and shown in the following Table 2.

TABLE 2 Softening point (° C.) of the obtained pitch Yield (%) Example 1270 38 Example 2 268 40 Example 3 281 35 Example 4 258 43 Example 5 32624 Example 6 344 25 Example 7 350 or more 27

(3) Preparation of Carbon Fiber

The carbon fiber was prepared through spinning, oxidation, andcarbonization processes, which is a general method, using the pitchprepared in Example 1.

SEM photographs of the carbon fiber prepared using the pitch synthesizedin the Example were shown in FIGS. 1 a (front view) and 1 b(cross-sectional view).

As shown in FIGS. 1 a and 1 b, in the case of using the pitch preparedunder the optimized synthetic conditions according to the presentinvention, sphere-shaped insoluble components were not formed, and thefinally prepared carbon fiber was isotropic.

(4) Experiments of Tensile Strength and Modulus of Elasticity of thePrepared Carbon Fiber

Tensile strength and modulus of elasticity of carbon fibers a1 to a10using the pitch synthesized in Example 1 were shown in the followingTable 3.

As shown in Table 3, in the case of using the pitch prepared under theoptimized synthetic conditions as in Example 1 of the present invention,it may be confirmed that the carbon fiber having excellent physicalproperties (average tensile strength of 1 GPa and modulus of elasticityof 56 GPa) was prepared.

TABLE 3 Maximum Tensile Tensile Modulus of elasticity load strengthstrain (Automatic Young's) (N) (GPa) (%) (GPa) a1 0.2341 1.0015 2.377745.6034 a2 0.1456 0.6228 1.8005 37.2215 a3 0.3232 1.3830 2.4544 58.7958a4 0.2087 0.8931 1.8943 48.2015 a5 0.2355 1.0078 1.5824 65.6378 a60.2800 1.1979 1.9017 63.4660 a7 0.1945 0.8321 2.7709 33.3722 a8 0.40291.7241 1.6097 116.6022 a9 0.2077 0.8886 1.8540 50.6760 a10 0.1586 0.67861.6505 42.0814 Average 0.2391 1.0229 1.9896 56.1658 Standard 0.08 0.330.40 23.77 deviation

With the method of preparing a pitch according to the exemplaryembodiment of the present invention, since the reactivity of petroleumresidues and C9 fraction is excellent, the high softening pointisotropic pitch may be obtained with the high yield without using aseparate catalyst.

Hereinabove, although specific embodiments of the present invention havebeen described, various modifications may be made without departing fromthe scope of the present invention. Therefore, the scope of the presentinvention should be not construed as being limited to the describedexemplary embodiments but be defined by the appended claims as well asequivalents thereto.

Although the present invention has been described with reference to thelimited embodiments, the present invention is not limited to theabove-mentioned embodiments but may be variously modified and changedfrom the above description by those skilled in the art to which thepresent invention pertains. Therefore, the scope and spirit of thepresent invention should be understood only by the following claims, andall of the equivalences and equivalent modifications to the claims areintended to fall within the scope and spirit of the present invention.

What is claimed is:
 1. A method of preparing a pitch for carbon fiber,the method comprising: a mixing step of mixing petroleum residues withC9 fraction to form a mixture; and a heating step of heating themixture.
 2. The method of claim 1, wherein the heating step is performedby multi-step heating in two steps or more.
 3. The method of claim 1,wherein the heating step includes: a primary heating step of primarilyheating the mixture; a secondary heating step of raising a temperatureafter the primary heating; and a tertiary heating step of raising atemperature after the secondary heating.
 4. The method of claim 3,wherein a heating temperature in the primary heating step is about 80°C. to about 100° C.
 5. The method of claim 3, wherein a heating time inthe primary heating step is about 1 hour to about 2 hours.
 6. The methodof claim 3, wherein in the primary heating step, a chain extensionreaction is induced.
 7. The method of claim 3, wherein a heatingtemperature in the secondary heating step is about 250° C. to about 300°C.
 8. The method of claim 3, wherein a heating time in the secondaryheating step is about ½ hour to about 2 hours.
 9. The method of claim 3,wherein in the secondary heating step, low boiling point materials areremoved.
 10. The method of claim 3, wherein a heating temperature in thetertiary heating step is about 320° C. to about 360° C.
 11. The methodof claim 3, wherein a heating time in the tertiary heating step is about3 hours to about 8 hours.
 12. The method of claim 3, wherein in thetertiary heating step, a condensation reaction occurs.
 13. The method ofclaim 1, wherein the petroleum residues include naphtha crackingresidues.
 14. The method of claim 1, wherein the petroleum residuesinclude pyrolyzed fuel oil (PFO).
 15. The method of claim 1, wherein thepetroleum residues comprise a substance from which low boiling pointmaterials are removed.
 16. The method of claim 1, wherein the C9fraction has aromaticity of about 40% to about 60%.
 17. The method ofclaim 1, wherein in the mixture, the C9 fraction is mixed at a contentof about 10 parts to about 50 parts by weight, based on 100 parts byweight of the petroleum residues.